As an electromagnetic clutch with a brake of this kind, there has been known, for example, one that is shown in FIG. 1 of Patent Document 1.
This electromagnetic clutch includes: a drive shaft; a driven shaft located concentrically with the drive shaft; a rotor which is integrally fixed to the driven shaft, and which has a clutch friction surface at a side surface on one side and a brake friction surface at a side surface on the other side; a magnetic pole body which has a coil and a coil bobbin for holding the coil, forms a magnetic circuit for a magnetic flux generated by excitation of the coil, and is fixed to a stationary member; a clutch armature which is so fixed as to be displaceable only in the axial direction relative to the drive shaft, is located opposite to the rotor, and is pressed against the clutch friction surface of the rotor by a magnetic attractive force generated by excitation of the coil; a brake armature which has a friction surface opposed to the brake friction surface of the rotor, and releases a braking action on the rotor by the magnetic attractive force generated by excitation of the coil; means for supporting the brake armature so as to be displaceable only in the axial direction in the magnetic pole body; and elastic means for causing the brake armature to give a braking action on the rotor only when the coil is not excited. The driven shaft in this case is assumed to be connected to a shaft in an applied apparatus such as a copying machine.
The brake function is added to the electromagnetic clutch used for paper feeding in a copying machine, a printer or the like, for the following reason. This kind of electromagnetic clutch is attached to a paper-feeding roller, and, when required, the clutch is engaged to effect paper feeding. Recently, the quality of papers to be used has been diversified. Especially where thick papers are used, a paper misfeeding may be generated in which paper is fed due to a flexure pressure, notwithstanding the clutch is disengaged. It is said that the brake function is added to the electromagnetic clutch in order to obviate such an error.
Incidentally, the electromagnetic clutch with the brake shown in Patent Document 1 operates as follows. When the coil is energized, a magnetic circuit due to a magnetic flux is formed which passes through the clutch armature, the rotor, the brake armature, the magnetic pole body, and the driven shaft, whereby the clutch armature is attracted onto the rotor. As a result, the torque of the drive shaft is transmitted through the clutch armature and the rotor to the driven shaft, and required driving such as paper feeding for the applied apparatus (not shown) is effected through the driven shaft. In this case, the brake armature is attracted onto the magnetic pole body against the springy pressure of the elastic means, so that the braking action on the driven shaft is being cleared. Next, when the energization of the coil is stopped, the clutch armature is released from the attraction onto the rotor, so that the rotor and, hence, the driven shaft will lose the drive force. Further, the brake armature is pressed against the rotor by the springy pressure of the elastic means and, therefore, a required braking force is applied to the driven shaft. In this manner, a measure for early stopping of the driven shaft attendant on de-energization is contrived.